Sensor plug

ABSTRACT

A sensor plug for use in sensing a plurality of operating conditions of a gearbox is disclosed. The sensor plug includes a body defining an axis. A probe end is formed at one end of the body and is particularly adapted for attaching to an oil drain plug of the gearbox. A plurality of sensors are located within the body for sensing operating conditions of the gearbox through the probe end. Examples of the sensors located within the body include a vibration sensor, a temperature sensor, and a pressure sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to monitoring systems for monitoring theoperation of a device, and more particularly to a sensor plug formounting sensors for use with such systems.

2. Related Art

In the ever-increasing competition in the industrial field, industrialequipment, such as rotating machinery, must operate at or near fullcapacity and sustain such operation for long periods of time. With thistype of demand placed on such equipment, periodic maintenance to avoid acatastrophic failure becomes important. Of course, periodic preventativemaintenance requires that the equipment be taken off-line for service,thereby potentially resulting in unnecessary down time. Maintenanceengineers have been challenged to establish proper time intervals forscheduled preventative maintenance in order to reduce such unnecessarydown time.

Alternatively, some maintenance engineers have concluded that theequipment should operate until catastrophic failure. This stems from thefact that, in some instances, it may be better to operate equipmentuntil it fails than to accept the maintenance and the resulting penaltycosts of shutting down the equipment prematurely. Also in lieu ofscheduled maintenance, some defects may be found by a trained operator.Because such detection is subject to human interpretation, pass/failcriteria may vary between operators and also from day to day with thesame operator. Other defects may not be detected at all.

Attempts have been made to automatically monitor such equipment fordefects through the use of a sensing element disposed within theequipment itself or through the use of a hand-held device which isperiodically attached to one or more discrete locations on the machinebeing monitored. More sophisticated monitoring systems are permanentlyinstalled and carry out essentially continuous monitoring of amachine-mounted transducer along with computer-based analysis of allmonitored data.

Most automatic monitoring systems typically sense vibration ortemperature. Vibration is produced by the moving parts in the rotatingmachinery due to causes such as unbalance, misalignment of shafts, wornout bearings, broken gear teeth or foreign particles lodged within themachine. Excessive levels of vibration indicate malfunction of themachine, which can result in machine failure. The temperature of abearing, for example, can also be monitored to detect the occurrence ofover-heating. In some instances, the oil level in the machine may bemonitored, automatically through the use of a float system or manuallythrough the use of a dipstick or a sight glass, so that the likelihoodof defects or malfunction of the device due to low oil level may bereduced. Other automatic means to detect oil level include beamtechniques that measure time of flight or frequency modulation of anultrasonic, microwave or light/laser beam. Electrical methods have alsobeen employed that detect changes in current, voltage, capacitance orinductance of the liquid to determine the fluid level.

The above-mentioned monitoring systems have certain disadvantages. Forexample, the sensor may be located remotely from the monitoring unit.This is undesirable for a number of reasons. First, the wire harnessbetween the monitor and the sensor is rather complex. In addition, thewire harness itself must be protected by passing the harness through anarmored braid or a metal or plastic conduit to prevent damage ordestruction.

Another disadvantage of the prior systems with regard to oil leveldetection is that the resulting measured value is often inaccurate,especially when utilizing a sight glass or a dipstick. With float-typeoil level sensors, the apparatus is rather complex and occupies arelatively large amount of space within the oil reservoir of themachine.

In addition, the ability to retrofit existing equipment with the newmonitoring system is limited. Because the sensor is remotely locatedfrom the monitor, installation is difficult, time-consuming, expensiveand may require a skilled operator to ensure all connections areproperly made.

SUMMARY OF THE INVENTION

One feature of the invention is an add-on or built-in component to adevice, such as a gearbox, to allow conditions within and around thedevice to be monitored in order to reduce failures in service, optimizemaintenance costs, and provide operating condition information thatovercomes the above and other disadvantages of conventional monitoringsystems. In one particular aspect of the invention, a sensor plug foruse in sensing a plurality of operating conditions of a device isdisclosed. The sensor plug includes a plug body and a probe end formedat one end of the body. The probe end is adapted for mounting to thedevice. A plurality of sensors is also included in the sensor plug andis located within the body. Each sensor senses an operating condition ofthe device. Accordingly, advantageously, the sensor plug may be adaptedfor mounting to an existing device or may be adapted for installationduring manufacture of the device. Additionally, locating one or moresensors in a sensor plug advantageously provides for ease of mountingthe sensors to the device.

In one embodiment, the sensor plug includes a well formed at an end ofthe body opposite the probe end. At least some of the sensors arelocated within the well. In another embodiment, the sensor plug furtherincludes a pressure port extending from the well through the probe end.A pressure sensor communicates with the pressure port. The pressuresensor may also communicate with ambient pressure. Thus, differential(gage) pressure may be detected. In another embodiment, the sensor plugmay include a temperature port extending from the well to the probe end.A temperature sensor is disposed within the temperature port. Thetemperature port is adapted to position the temperature sensor to senseoil temperature or case temperature of the device. In an alternativeembodiment, the temperature port extends through the probe end and atemperature port plug is inserted into and extends partially within thetemperature port. This effectively seals the probe end such that fluidis prevented from leaking through the temperature port. In a preferredembodiment, the temperature port plug is formed of a thermallyconductive material. The sensor plug may also include a vibrationsensor. The vibration sensor may be mounted in the well to detectvibration in the device.

In another embodiment, the well of the sensor plug is filled with apotting material to encapsulate the sensors. An ambient pressure portmay be formed through the potting material so that pressure sensor maycommunicate with the ambient pressure. In a preferred embodiment, thesensor plug also includes a retainer for retaining the potting materialwithin the well. Preferably, the well defines an axially extendingsidewall having the retainer formed therealong for axially retaining thepotting material within the well. In one instance, the sidewall isformed with a coarse surface, thereby defining the retainer.Alternatively, the sidewall may include a radially inwardly extendinglip to define the retainer.

The sensor plug may also include a shoulder formed between the probe endand the well. The shoulder is adapted to axially support a housing for aprocessing unit such that the well may extend into the housing. Whenattached thereto, the leads from the sensors emerging from the well areconnected directly to the processing unit mounted within the housing,thereby enclosing each lead entirely within the housing. A seal may alsobe disposed adjacent the shoulder for sealing against the housing. In apreferred embodiment, the shoulder is positioned in a spacedrelationship with respect to the case of the device and the probe end soas to support the housing in a spaced relation away from the sidewall ofthe device.

In an embodiment of the invention, the probe end is adapted forcommunication with an oil reservoir of the device. Preferably the probeend is adapted attaching to an oil drain hole.

In another embodiment, the body is formed of at least one materialselected from the group consisting of metal, plastic and ceramic.

In yet another aspect of the invention, the sensor plug includes a plugbody adapted for mounting to the device and a support formed on the plugbody. The support is adapted for mounting a housing for a processingunit to the sensor plug.

Various embodiments of the present invention provide certain advantagesand overcome certain drawbacks of the conventional techniques. Not allembodiments of the invention share the same advantages and those that domay not share them under all circumstances. Further features andadvantages of the present invention, as well as the structure andoperation of various embodiments of the present invention, are describedin detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings, in which:

FIG. 1 is a perspective view of a device, such as a gearbox, for usewith the present invention;

FIG. 2a is a cross-section taken along line 2—2 of FIG. 1 when thegearbox is not in operation;

FIG. 2b is a cross-section taken along line 2—2 of FIG. 1 when thegearbox is in operation;

FIG. 3 is an enlarged perspective view of a sensor plug for use with thepresent invention;

FIG. 4 is a cross-sectional view taken along line 4—4 of FIG. 3;

FIG. 5a is an enlarged view of an alternative embodiment of the areaencircled by line 5 a of FIG. 4;

FIG. 5b is an enlarged view of an alternative embodiment of the areaencircled by line 5 b of FIG. 4;

FIG. 6 is an enlarged view of an alternative embodiment of the areaencircled by line 6 of FIG. 4;

FIG. 7 is an enlarged view of an alternative embodiment of the areaencircled by line 7 of FIG. 4;

FIG. 8 is a diagrammatic representation of an example of a processingunit for use with the present invention;

FIG. 9 is a flow chart showing an example of pressure sensor analysis;

FIG. 10 is a flow chart showing an example of sensor diagnostics;

FIG. 11 is an example of a tabular output of the diagnostics performedin FIG. 10;

FIG. 12 is a flow chart showing an example of vibration sensor analysis;

FIG. 13 is a frequency response diagram showing an example of an outputof a vibration sensor;

FIG. 14 is a flow chart showing an example of false alarm control forvibration;

FIG. 15 is a flow chart showing an example of false alarm control forother sensed parameters;

FIG. 16 is a flow chart showing an example of threshold settinganalysis;

FIG. 17 is a flow chart showing an example of operating margin analysis;

FIG. 18 is a flow chart showing an example of torque estimation;

FIG. 19 is a sample curve showing a relationship between a number ofdiscrete samples per revolution and torque; and,

FIG. 20 is a flow chart showing an example of active gearbox control.

DETAILED DESCRIPTION

Referring now to FIG. 1, which is a perspective view of an example of agearbox for use with the present invention, and FIGS. 2a and 2 b, whichare cross-sectional views of the portion of the gearbox taken along line2—2 of FIG. 1 during inoperation and operation of the gearbox,respectively, a monitoring system 100 is shown attached to the gearbox102. Although the invention described herein is discussed withparticular reference to a gearbox, it is to be appreciated that anydevice or machine that is required to be monitored may be used with thesystem of the present invention.

The gearbox 102, which may be a conventional gearbox, includes a case104 for encasing a speed reducing gear train (not shown). An input shaft106 is connected to one side of the gear train and an output shaft 108is connected to another side. Cooling fins 110 are formed on the case104 of the gearbox 102 to allow for convective cooling. A plurality ofmounting pads 112 may be used to secure the gearbox 102 in a suitablemanner. The gearbox 102 may also include a breather element 114 formedthrough a side wall of the case 104 to prevent pressure buildup insidethe gearbox 102. Such an increase in pressure may ultimately result inundesirable oil leakage past the shaft seals 118, 120.

Conventional gearboxes include at least one oil drain plug for drainingoil contained therein and many gearboxes include more than one drainplug because the gearbox may be mounted in any desired orientation.Thus, in order to fully drain the oil from the gearbox, the drain plugshould be below the oil level.

According to one aspect of the present invention, as best shown in FIGS.2a and 2 b, a sensor plug 130 may be adapted for attaching to an oildrain plug 132 of the gearbox 102 that is below the surface level 134 ofthe oil reservoir 136 at a predetermined depth “H”. As will be fullyexplained hereinafter, a plurality of sensors for sensing operatingconditions of the gearbox is located in the sensor plug 130. When thegearbox is not operating (i.e. the input shaft 106 is not receivingpower), the oil level 134 in the gearbox is a substantially flat, levelsurface and assumes a height designated as “H” relative to the sensorplug 130. However, as shown in FIG. 2b, when power is being delivered tothe input shaft, the rotating geartrain within the gearbox causes theoil level 134 to deviate from a level surface and assume the shape of anangled surface, which may be a curved surface, as shown, a flat butinclined surface, or an irregularly perturbed surface. The amount ofdeviation may be a function of the characteristics of the oil as well asthe speed of the gearbox. Other parameters, such as temperature, mayalso effect the amount of deviation. As a result, the height decreasesto a level “H₁” relative to the sensor plug 130. Of course, the liquidlevel may rise, depending upon the direction of rotation of thegeartrain as well as other parameters, such as internal restrictions,etc. Suffice it to say that the height is likely to change when thegearbox is powered. As used herein, the term “amount of deviation” shallmean the amount of increase or decrease in height of the oil level at acertain point on the liquid surface relative to the height of the oillevel when the gearbox is not in operation.

The monitoring system 100 also includes a processing unit 140, typicallyimplemented as a printed circuit board, mounted within a housing 142.The housing may be formed of any suitable material to withstand theoperating environment of the gearbox. The processing unit 140 iselectrically coupled to the plurality of sensors within the sensor plug130 for receiving signals therefrom and for analyzing the signals toprovide useful information as to the condition of the gearbox, as willbe explained fully hereinafter. The housing 142 is preferably mounteddirectly to the sensor plug 130 and completely contains the electricalleads 144 of the plurality of sensors emerging from the sensor plug,thereby obviating the need for an external protected wire harness. Aportion of the sensor plug extends into a hole 146 formed in the housing142 and holds the housing 142 a distance away from the wall 116 of thegearbox so as to allow convective airflow between the housing and thecooling fins of the gearbox 102 for adequate cooling. The housing 142may also include one or more connectors 148 (see FIG. 1), which areelectrically connected to the processing unit 140, for communicationwith a network in which to relay one or more sensed operating conditionsto a host computer. Each sensor may communicate independently with thenetwork or the host computer through a dedicated communication link forthat sensor. Power to the processing unit 140 and the sensors may besupplied through the network connectors 148.

Alternatively, the monitoring system 100 may function as a stand-aloneunit in which the processing unit indicates the operating conditions ofthe gearbox through an indicator for example indicator 149. In oneparticular example, the indicator 149 may include one or morelight-emitting diodes (LEDs) or a liquid crystal display (LCD) toindicate one or more status levels of the gearbox, such as “POWER ON”,“NORMAL”, “CAUTION” or “WARNING”. Alternatively, the indicator mayinclude a CRT displaying a graphical user interface (GUI) of the LCD maydisplay the GUI.

Although not shown, rather than housing the processing unit in aseparate housing that is mounted to the sensor plug, the processing unitmay be housed within the sensor plug itself. In this example, thecommunications connectors would be disposed on the sensor plug.

Referring now to FIG. 3, which is a perspective view of the sensor plug130, and FIG. 4, which is a cross-sectional view of the sensor plug 130taken along line 4—4 of FIG. 3, the sensor plug 130 includes a body 160having one or more sensors housed therein for sensing operatingconditions of the gearbox. In one particular example, the sensor plug130 houses a pressure sensor 162, a temperature sensor 164 and avibration (or noise) sensor 166, although it is to be appreciated thatother sensors may be added or substituted.

The body 160 may be formed of any one or more suitable temperatureresistant, rugged materials, such as plastic, metal or ceramic, in anysuitable form, provided that the sensor plug may be readily attached tothe gearbox. The sensor plug may also be fabricated using any suitableprocess such as molding, machining or casting. Preferably, the body 160is formed of a plastic material having a generally longitudinallyextending cylindrical shape defining a longitudinal axis 168. The sensorplug includes a probe end 170 at one end of the body 160, which isadapted for attaching to the gearbox, specifically to the oil drain plug132 as previously mentioned. The probe end may be adapted such that itmounts flush with the interior wall of the case. A thread 172 may alsobe formed on the body at the probe end to facilitate attachment to thegearbox. This thread may be an N.P.T. thread to seal the sensor plug tothe case or, alternatively, may be a straight thread with appropriatesealing means such as an O-ring or the like. In this particular example,the probe end is formed with a ¾ inch N.P.T. thread to match that of theoil drain plug. Adapting the sensor plug for attaching to the oil drainplug also readily facilitates quick removal and repair or replacement ofany or all of the sensor(s) housed in the sensor plug or the sensor plugitself without undue complication.

The body 160 also includes a well 174 at another end of the bodyopposite the probe end 170 for containing one or more sensors. The well174 may be defined by an axially extending sidewall 176 and a bottomwall 178 to shield the sensors. The body 160 fier includes a shoulder180 formed between the probe end 170 and the well 174. The shoulder 180may be adapted to axially support the housing 142 such that the well 174may pass through the hole 146 formed in the housing and extend into thehousing 142 (see FIGS. 2a and 2 b).

The well 174 may include a threaded section 182 formed on the outersurface thereof to receive a nut 184 in order to secure the housing 142to the sensor plug 130. Of course, any suitable means for attaching thehousing to the sensor plug may be employed. A groove 186 may also beformed between the shoulder 180 and the well 174 to receive either anO-ring or other sealing means such that the housing 142 may firmly sealonto the sensor plug 130.

As previously mentioned, the sensor plug 130 may house the processingunit 140. In this example, the well 174 may be adapted to receive theprocessing unit 140.

To facilitate attachment of the sensor plug 130 to the gearbox 102, theouter surface of the shoulder 180 may be formed with an installationtool surface 188. In a preferred embodiment, the outer surface is formedwith flats, which may be in the form of a square or hex, to facilitateengagement with a wrench. It should be appreciated that the installationtool surface may be formed as any suitable surface in any suitablelocation in or on the body 160. For example, the installation toolsurface may be formed of the probe end 170 or on the well 174. If formedon the well, the installation tool surface may be formed as any suitablyshaped socket, such as a hex socket, a splined socket, a square socket,or the like. The sensor plug 130 may also be mounted to the gearboxthrough the use of a bonding agent such as a weld, solder or an epoxy,in addition to or instead of the threads.

Continuing with reference to FIG. 4, the sensor plug 130 may alsoinclude an axially extending pressure port 190 extending from the well174 through to the probe end 170. The pressure sensor 162 communicateswith the oil within the gearbox. Thus, the pressure sensor communicateswith the pressure port 190. Those skilled in the art will recognize inview of this disclosure that the pressure sensor 162 may be mountedanywhere along the pressure port 190. Preferably, the pressure sensor162 is mounted within the well 174 with any suitable epoxy or attachmentmeans to sealingly secure the pressure sensor 162 to the pressure port190.

In a preferred embodiment, the pressure sensor 162 is a piezoresistivesensor that can sense an oil pressure (“head”) in a range from about0.12 psi (for a relatively small gearbox) to about 1.86 psi (for arelatively large gearbox). Further, the pressure sensor should be ableto detect a drop in oil pressure equivalent to about 1 inch (0.03 psi)when the gearbox is filled with an oil having a specific gravity of0.849 (such as Mobil HC 634 Uptime oil). The pressure sensor should alsobe able to sense an increase in pressure of 0.1 psi above the oilpressure with a full oil reservoir (which is indicative of a cloggedbreather element). An example: of such a pressure sensor capable ofmeeting the above mentioned requirements is item number CPC-Cmanufactured by Data Instruments, Inc. of Sunnyvale, Calif., U.S.A. Thepressure sensor requires an excitation of 4 to 16 volts DC. The sensorproduces a differential voltage output of 23 millivolts for one poundper square inch with a 15 volt DC stimulus The interface electronicsrequires a differential input with voltage amplification and signalfrequency cutoff above 10 hertz. A low pass filter may be used toincrease noise voltage immunity.

Although not shown, a diaphragm may be mounted between the pressuresensor and the pressure port. Also, rather than provide a separatediaphragm, the pressure port may be formed as a blind hole having a thinwall section defining the transition between the pressure port and thewell. The pressure sensor may then be mounted directly to this wall. Inoperation, this wall would act as a diaphragm and would also act as aseal between the pressure sensor and the pressure port. Of course, it isto be appreciated that producing a thin wall that would act as adiaphragm may only be practical when the sensor plug is formed ofcertain materials.

In an alternative embodiment, as shown in FIG. 5a, a diaphragm 191 madeof a suitable material may be placed over the pressure port at the probeend so that the diaphragm may be in contact with the oil in the gearboxwhen the sensor plug is attached to the gearbox. An incompressibleliquid 193, such as oil, may be placed in the pressure port between thediaphragm 191 and the pressure sensor 162. In this manner, as thediaphragm deflects due to the oil pressure in the gearbox, the liquidpressure in the pressure port also increases, thereby triggering thepressure sensor. This embodiment may be advantageous because the sensorplug and the pressure sensor may thus be immune to sludge build-up inthe oil reservoir of the gearbox.

As previously mentioned, a temperature sensor 164 may be included withinthe sensor plug 130 to detect the temperature within the gearbox.Specifically, the temperature sensor 164 may be used to sensetemperature indicative of gear overheating or bearing overheating. Othertemperature information may be used in various ways as desired, some ofwhich will be described hereinafter. In one embodiment, the temperatureinformation may be used to determine whether the gearbox is operatingwithin its recommended temperature range, as supplied by the gearboxmanufacturer. In another embodiment, the temperature information may beused to establish a rate of change of temperature, which may be used toindicate or predict various operating conditions.

In this example, the body 160 of the sensor plug 130 includes atemperature port 192 extending from the well 174 to the probe end 170.In the example shown in FIG. 4, the temperature port 192 extends throughthe body 160 to provide a thermally conductive path to the oil. Atemperature port plug 194 may be inserted at the probe end of thetemperature port so as to extend partially into the probe end to sealthat end of the temperature port. Preferably, the temperature sensor 164is disposed within the temperature port 192 and is used to detect theoil temperature within the gearbox. It is to be appreciated that thetemperature port plug may finally rest at any suitable location alongthe temperature port so as to act as a seal between the oil reservoir ofthe gearbox and the temperature sensor. In one embodiment, the sensorplug is at least ⅛ inch long.

In a preferred embodiment, the temperature port plug 194 is formed of athermally conductive material so that the temperature sensor 164 mayreadily determine the temperature of the oil and the gearbox. Inaddition, the temperature port plug 194 may be press-fit into thetemperature port to seal the temperature port. Of course, those skilledin the art will recognize in view of the disclosure that other fasteningmeans may be used, such as for example, the use of an epoxy or threads.Alternatively, any suitable seal, such as an epoxy seal, may be formedbetween the oil reservoir of the gearbox and the temperature sensor.

In an alternative embodiment, as shown in. FIG. 5b, the temperature port192 may be formed as a blind hole having an end wall 196 at the probeend 170 wherein the temperature port 192 does not extend completelythrough the body 160. In this example, however, the end of thetemperature port may be formed of the same material as the body itself.In one embodiment, the end wall is at least ⅛ inch thick.

Rather than sense the oil temperature, the sensor plug may be configuredsuch that the temperature sensor is positioned to sense the temperatureof the case of the gearbox. In such an example, as shown in FIG. 6, thesensor plug 130 may include a radially extending port 200 extending fromthe temperature port 192 through the threaded section 172. Thetemperature sensor 164 may be placed through the radial extending port200 to readily sense the case temperature.

In a preferred embodiment, the temperature sensor 164 is a semiconductorsensor that is able to operate in a range between about −40° F. to about200° F. with an accuracy of about +/−5° F. and with a response time ofless than about 5 minutes. An example of such a temperature sensorcapable of meeting the above mention requirements is item numberLM35CZ-ND manufactured by the National Semiconductor Corporation ofSanta Clara, Calif., U.S.A. This sensor requires a 4 to 30 volt DCstimulus and produces 10 millivolts per degree Celsius. An amplifier maybe used to raise the voltage to a range that corresponds with the inputrange of an analog-to-digital converter. Due to the relatively largethermal masses involved, the signal of interest may be a slow varying DClevel with frequency content up to a few hertz. The signal may be fedthrough a low pass filter with a cut off frequency of approximately 10hertz in order to minimize the influence of noise (especially 60 hertz)in temperature measurements.

As previously mentioned, the sensor plug 130 may also include avibration sensor 166, which (as best shown in FIG. 4) may comprise anysuitable transducer and which may be disposed along any suitable surfacewithin the well 174, such as the bottom wall 178 or the sidewall 176.Alternatively, the vibration sensor 166 may be mounted on an externalsurface of the body 160. Preferably, the vibration sensor is mounted tothe bottom wall 178 of the well 174. Mounting at this location has thedesirable effect of sensing horizontal vibration of the gearbox wall 116when the sensor plug 130 is mounted thereto. Preferably, the vibrationsensor is a piezoelectric accelerometer and should be able to detect abearing frequency of about 300 Hz with a 6 th harmonic frequency ofabout 1800 Hz and a gear frequency of about 500 Hz. An example of such avibration sensor capable of meeting the above mentioned requirements isitem number A5100-01 manufactured by Oceana Sensor Technologies, Inc. ofVirginia Beach, Va., U.S.A. The sensor requires a voltage stimulus of 18to 28 volts DC with a constant current source of 2 to 20 milliamps. Theoutput of the sensor is 0.1 volt per g of acceleration. The signalconditioning for the accelerometer amplifies the voltage level in orderfor the analog-to-digital converter to be sensitive to the accelerationlevels found in the vibration of a gearbox and its associatedcomponents. The accelerometer has a frequency response from 0.1 hertz upto 10,000 hertz. A low pass filter with a cutoff frequency of 10,000hertz may be used to eliminate any aliasing of the signal when thesignal is digitized at a rate above the Nyquist frequency of 20,000hertz. It is to be appreciated that a noise sensor, such as a microphoneor an ultrasonic transducer, may be used in place of the accelerometer.

In order to protect and secure the sensors within the sensor plug, apotting material 202, such as an epoxy, may be placed within both thewell 174 and the temperature port 192, as shown in FIG. 4. It may bedesirable that the pressure sensor 162 be exposed to both the pressurein the gearbox as well as to ambient pressure. To achieve this resultwhen a potting material is used, an ambient pressure port 204 may beformed in the potting material 202. This may be accomplished by anysuitable method including drilling a hole after the potting material isplaced in the well, or alternatively, placing a tube adjacent thepressure sensor as the potting material is poured into the well.

To effectively hold the potting material 202 within the well, a retainermay be provided. In one particular example, the retainer is formed inthe body itself. For example, as shown in FIG. 7, the sidewall 176 ofthe well 174 is provided with a coarse surface 204, such as a knurledsurface. Thus, the potting material 202 may effectively attach to thesidewall 176, thereby reducing the likelihood that the potting materialwill dislodge from the well 174. Alternatively, also shown in FIG. 7,the outer end 206 of the well 174 may be formed with a radially inwardlyextending lip 208. Once the potting material 202 is placed in the well174, flows under the lip 208 and hardens, it may be effectively retainedtherein.

Further, although not shown, other retainers may be used. One suchretainer may be in the form of a cap secured over the well 174 ontothreads 182. Alternatively, the retainer may be formed as a plug whichengages the sidewall 176. Those skilled in the art will recognize otherretainers suitable for retaining the potting material in the well.

Turning now to FIG. 8, a diagrammatic representation of the processingunit 140 of the system 100 coupled to the sensors and the gearbox isshown. It is to be appreciated that the system 100 may be embodied in astand-alone unit in which case, the system program may be programmedinto processing unit 140, as shown in FIG. 8, or may be embodied in aremote host computer (not shown), in which case, the system program maybe programmed onto a hard-drive or other magnetic or optical medium. Ofcourse, the processing unit may communicate with a storage medium suchas a magnetic or optical medium, which may be programmed with the systemprogram. In the example shown, the processing unit 140 includes a CPU220, ROM 222, RAM 224 as well as an I/O bus 226, which may have 111general purpose I/O lines. In addition to various computer codes thatmay make up the system, the ROM 222 may also include a look-up table228. In a preferred embodiment, the table 228 may include temperature asa function of density for a given oil contained in the gearbox, whichmay be necessary for a certain computation as will be discussedhereinafter.

The sensors 162, 164, 166 are coupled to the processing unit 140 via I/Obus 226. The sensor signals may be passed through a filter, which may bea low pass filter, to an analog-to-digital converter 229 before beingprocessed by the CPU 220. The CPU may have a 16 bit architecture with a20 megahertz clock rate. The CPU may also communicate with a storagedevice to store historical data of sensed and/or determined operatingconditions. An example of a suitable CPU is item number SAB-C167CR-LMmanufactured by the Siemens Corporation of Germany. Theanalog-to-digital converter has a resolution 12 bits. The processingunit may include a CAN interface, two RS-232 ports, watchdog timer, and5 timers. ROM memory may be used to download executable code to FLASHtype memory and EEPROM type memory to store variables utilized by theexecutable code. The FLASH type memory may also used for long term datahistory storage. The analog-to-digital converter, the band pass filterand any other necessary components between the sensor and the CPU,together with the interconnecting signal lines define a sensor circuit.

As previously mentioned, the processing unit may communicate with anetwork 230 through connectors 148. In a preferred embodiment, theprocessing unit may communicate with the host computer via the RS-232serial port and may operate autonomously with simple discrete logicoutput for alarming and/or analog communication via a 4-20 milliampcurrent loop. Alternatively, the processing unit may communicate throughone or more fieldbus networks in order to accommodate modern productionfacilities with installed fieldbus networks. Examples of such a fieldbusnetwork is a DeviceNet network, provided by the ODVA Organization ofCoral Springs, Fla., U.S.A. or a Profibus network provided by theSiemens Corporation of Karlsruhe, Germany. These fieldbuses enable dataexchange between intelligent devices distributed over a plant floor.

It is to be appreciated that the processing unit performs a plurality offunctions, some of which may require comparisons between sensed valuesand thresholds and determinations based on whether the sensed valueshave exceeded or crossed the thresholds. Thus, as used herein, the terms“exceeded”, “crossed”, “greater than” or “less than” or any other termused to describe relative value are used interchangeably to mean thatthe sensed value has increased above a threshold value or that thesensed value has decreased below a threshold value, depending upon thepolarities of the threshold value and the sensed value being comparedand whether the sensed value is expected to increase or decrease.

In a preferred embodiment, an ambient temperature sensor 231 is coupledto the processing unit and is housed in the housing 142, preferably at alocation away from the gearbox 102 and preferably on the outer housingwall, as shown in FIGS. 2a and 2 b. An example of an ambient temperaturesensor is item number LM35CZ-ND manufactured by the NationalSemiconductor Corporation of Santa Clara, Calif., U.S.A. In someembodiments, the processing unit receives both the ambient temperaturefrom the ambient temperature sensor 231 and the oil temperature or thegearbox case temperature from temperature sensor 164 to derive adifferential temperature, which may be compared to prescribed ranges asdetermined by the gearbox manufacturer.

In another aspect of the invention, the processing unit 140 may bepre-programmed with a set of instructions for carrying out at least someof the steps shown in FIG. 9. Initially, when the gearbox is notreceiving power, at step 300, the oil pressure is sensed. It also is tobe appreciated that, although the example described herein discloses anoil pressure sensor housed within a sensor plug, according to thisaspect of the invention, the oil pressure sensor may be placed in anysuitable housing, or no housing at all, provided that the oil pressuresensor can sense static oil pressure (“head”) within the gearbox. Atstep 302, the oil level is determined based on the oil pressure. Oillevel monitoring may be performed to detect oil loss due to a variety ofreasons.

The oil level may be determined using the following equation:

P=ρgH+P _(A)  [1]

where,

P=Sensed pressure

ρ=Density of the oil at a certain temperature;

g=Gravitational constant;

H=Height from the level of the pressure sensor to the surface of theoil; and,

P_(A)=Pressure above the oil level (e.g., atmospheric pressure)

Thus,

H=(P−P _(A))/(ρg)  [2]

With the oil temperature known, either through sensed temperature fromtemperature sensor 164, through an inferred temperature or through anassumed temperature stored in memory (i.e., ambient temperature), usingthe temperature density table 228 stored in ROM 222, the density may bereadily determined. Given that the density and gravitational constantare known, that the pressure (P) is sensed and that the pressure abovethe oil level (P_(A)) may be assumed to be atmospheric, the height ofthe liquid level may be readily calculated using, for example, Equation[2]. Alternatively, a table of oil level as a function of oil pressuremay be stored in ROM 222. The table may be compiled using the density ofthe oil (ρ) at a predetermined or assumed temperature. Also, a number oflook-up tables may be provided, each based on a different oil density.

It should be appreciated that the pressure sensor 162 used in theexample described herein is a differential pressure sensor because thesensor senses atmospheric pressure through ambient pressure port 204.Thus, pressure sensor 162 actually senses (P−P_(A)) and a directmeasurement or assumption of P_(A) is not required. Of course, anabsolute pressure sensor may be used, in which case, atmosphericpressure may be sensed with another pressure sensor or an assumedatmospheric pressure (P_(A)) may be stored in ROM 222. The processingunit then calculates (P−P_(A)). The determined oil level may beindicated through, for example, indicator 149. Also, the oil level maybe stored in memory to provide a history of the oil level. Thus, a rateof change in oil level may be indicated and used for predictiveanalysis, for example, by indicating when to add to or change the oil.In addition, a drop in oil pressure (i.e. a drop or absence of a signalfrom the pressure sensor) may be indicative of sludge build-up in thepressure port 190.

Rather than indicate the actual oil level, the processing unit mayindicate whether the oil level is below a certain level. Thus, at step304, the calculated oil level obtained in step 302 is compared with astored threshold level. If the calculated oil level is different fromthe threshold, then, at step 306, the processing unit 140 indicates anincorrect oil level signal. It is to be appreciated that the method ofthe present invention described herein may detect a low oil level or ahigh oil level. In addition, it is to be appreciated that the thresholdlevel may include some amount of tolerance, or bandwidth, in which acorrect oil level may be indicated. Those skilled in the art willrecognize in view of this disclosure that rather than rigorously performthe calculation of the actual oil level, the sensed pressure (P) may becompared directly to a desired threshold pressure (P_(D)), which may becalculated based on a desired threshold oil level (H_(D)).

If the oil level is correct, at step 308, the processing unit may signalthat the gearbox is ready for operation. However, in a preferredembodiment, the absence of a warning suffices as an indication that thegearbox may be operated. During operation, as indicated at step 310, theprocessing unit 140, through the sensor 162, continues to monitor oilpressure. Also, the processing unit may continue to monitor otherparameters, such as temperature, through sensor 164, and vibration,through sensor 166. Again, using either Equation [1] or Equation [2] ora look-up table, the oil level is determined at step 312.

At step 314, the oil level is compared to a threshold value. Because thegearbox is in operation and, as previously mentioned, the amount ofdeviation of the oil level may be a function of one or more gearboxoperating states, such as speed or temperature for example, thethreshold level may be adjusted to one or more new threshold values.Each new threshold value represents a desired oil level at a particularspeed and/or temperature, for example. These new threshold values may berepresented as discrete values or may be represented as a continuousfunction, and may be stored in the memory of the processing unitaccordingly (i.e., as a look-up table or as an equation). Of course,each new threshold value may include some amount of tolerance, orbandwidth. If the determined oil level is different from the threshold,then, at step 316, the processing unit 140 generates an incorrect oillevel indication.

It is to be appreciated that any suitable method to determine the speedof the gearbox may be used to determine the amount of deviation of oillevel when the gearbox is in use. One such example is through the use ofa speed sensor 900 (see FIG. 1) to sense any rotating component withinthe gearbox. Alternatively, the speed may be extrapolated frominformation derived from the vibration sensor.

It has been found, however, that it may not be necessary to adjust thesecond threshold based upon the speed of the gearbox. During operationof the gearbox at its rated capacity, the amount of deviation of oillevel may be insignificant, especially in relatively large gearboxes.Thus, the tolerance or bandwidth of an acceptable oil level may be largeenough to accommodate the relatively small amount of deviation in oillevel.

The processing unit 140 used in the present invention may also detectwhether the breather element 114 (see FIG. 1) is clogged. When thebreather element is clogged, the pressure in the gearbox above the oilundesirably increases which may result in oil leakage past the shaftseal. The pressure increase may be primarily due to the increasingtemperature in the gearbox, which may occur during operation.

Thus, continuing with reference to FIG. 9, at step 318, the processingunit 140 determines the pressure above the oil by sensing the oilpressure (P) and subtracting the desired pressure (P_(D)), (which is theoil pressure when the oil level is at the threshold value) to obtain acalculated pressure (P_(C)). This calculated pressure (P_(C)) iscompared with atmospheric pressure (P_(A)) at step 320 to determinewhether the sensed pressure is too high. If the calculated pressure(P_(C)) is greater than atmospheric pressure (P_(A)), then, at step 322,the processing unit 140 indicates that the breather element 114 isclogged.

It should be appreciated that because the pressure sensor 162 used inthe example described herein is a differential pressure sensor, ratherthan subtracting the atmospheric pressure (P_(A)), a direct comparisonmay be made between the sensed pressure (P) and the desired pressure(P_(D)). If the sensed pressure (P) is greater than the desired pressure(P_(D)), a clogged breather element may be indicated. In another aspectof the invention, the processing unit 140 may indicate when to changethe oil in the gearbox. This may be accomplished by determining theamount of time that the gearbox has been operating since the previousoil change.

According to yet another aspect of the invention, in some instances, itmay be desirable to determine whether a sensor is malfunctioning.Otherwise, it is possible that a false indication of gearbox malfunctionmay be made, or the system may fail to detect a malfunction. In order todetermine whether the sensors are operating properly, the system 100,through the processing unit 140, for example, performs a self-diagnostictest as exemplified in the steps shown in FIG. 10. Initially, during oneoperating state when the sensors are de-energized but the processingunit is energized, at step 400, a signal noise level threshold (ρ) isreceived by the processing unit and is stored in memory. The signalnoise level threshold (ρ) represents the sensor noise itself as well asthe sensor channel noise, which represents the noise between the sensorand the CPU. Rather than receive the signal noise level threshold (ρ),the signal noise level threshold (ρ) may be pre-set and stored inmemory. This may be possible because the sensor noise level thresholdmay be known for the sensors and the sensor channel noise may bedetermined during manufacture of the processing unit.

At step 402, in another operating state, the sensors are energized andthe gearbox operation is monitored. The sensor signals may becontinuously monitored or may be periodically sampled to produce asensed signal (μ). At step 404, the sensed signal (μ) is compared to therespective noise level (ρ) generated in step 400. Using the followingset of Rules, a sensor status value (H) may be generated.

H _(T)=0, when μ_(T)≧ρ_(T)  [3]

H _(T)=1, when μ_(T)<ρ_(T)  [4]

where,

H_(T)=Temperature sensor status;

μ_(T)=Sensed temperature;

ρ_(T)=Temperature signal noise;

0=Sensor is malfunctioning; and,

1=Sensor is functioning.

H _(P)=0, when μ_(P)≧ρ_(P)  [5]

H _(P)=1, when μ_(P)<ρ_(P)  [6]

where,

H_(P)=Pressure sensor status;

μ_(P)=Sensed pressure;

ρ_(P)=Pressure signal noise;

0=Sensor is malfunctioning; and,

1=Sensor is functioning.

H _(V)=0, when,μ_(V)≧ρ_(V)  [7]

H _(V)=1, when μ_(V)<ρ_(V)  [8]

where,

H_(V)=Vibration sensor status;

μ_(V)=Sensed vibration;

ρ_(V)=Vibration signal noise;

0=Sensor is malfunctioning; and,

1=Sensor is functioning.

At step 406, a determination is made as to whether any sensor is faultyand, if so, which one. This may be accomplished, for example, bycomparing a sensor status value of one sensor with the sensor statusvalue of another sensor to determine a malfunctioning sensor.

The possible combinations of sensor status values are depicted in FIG.11. Thus, for example, if the temperature sensor status (H_(T)) has avalue of 0, indicating that the sensed temperature is less than thenoise level (i.e., the temperature sensor is malfunctioning), and thepressure sensor status (H_(P)) has a value of 1, indicating that thesensed pressure is greater than a noise level (i.e., the pressure sensoris functioning properly), and the vibration sensor (H_(V)) status alsohas a value of 1, indicating that the sensed vibration is greater than anoise level (i.e., the vibration sensor is functioning properly), thenthe processing unit is able to determine that the temperature sensor isfaulty because it returned a sensor status value different from thesensor status value of the other two sensors. Of course, the matrix ofFIG. 11 may be larger or smaller, depending upon the number of sensorsused.

Similarly, if H_(T)=1 and H_(V)=1, but H_(P)=0, then it can be assumedthat the pressure sensor is faulty. The same analysis holds with respectto the vibration sensor. Thus, if H_(T)=1 and H_(P)=1, but H_(V)=0, thenthe vibration sensor is deemed faulty. Of course, if H_(T)=1, H_(P)=1,and H_(V)=1, then an indication of normal operation may be provided, or,preferably, no indication is provided. Also, if H_(T)=0, H_(P)=0 andH_(V)=0, then the processing unit is able to determine with a fairamount of certainty that the sensors are functioning properly but thatthe sensors are de-energized. The level of certainty rises because theprobability of all three sensors simultaneously malfunctioning is low.

There are three situations where it becomes more difficult to detectwhich sensor, if any, may be malfunctioning. This occurs when two of thesensors status values (H) each indicate a value of 0 and the otherindicates a value of 1. In this situation, processing unit 140 may usestatistical analysis to determine whether or not one or both of theindicated sensors is malfunctioning. An example of such statisticalanalysis may include a mean-time-to-failure analysis for a certainsensor. Thus, if, for example, H_(V)−0,and H_(T)=0, yet H_(P)=1, thenthe mean-time-to-failure of the temperature sensor and themean-time-to-failure of the vibration sensor are separately determined,and each is compared with its running time. If either of the sensorshave operated beyond a mean time to failure, then an indication ofsensor failure of that particular sensor may be made. Another example ofa statistical analysis may be a statistical trending analysis in whichthe failure of a sensor may be based upon historical data accumulated inthe memory of the processing unit. Of course, other suitable analysismethods may be used.

It should be appreciated that the sensed parameter (μ), whether it betemperature, pressure or vibration, may be based on an average of aplurality of samples. In a preferred embodiment, 100 or more samples arerecorded to determine an average value for (μ). It should also beappreciated that the noise level thresholds (ρ) may include a range ofvalues indicative of an acceptable range of normal operating conditions.

The processing unit may also determine whether any one of the sensors isin an open or short circuit condition. If the sensor is in a shortcircuit condition, the sensed signal (μ) may be at a maximum value,which would indicate that the sensed condition is uncharacteristicallyhigh. The probability of such an occurrence is typically low, thus, itis reasonable to conclude that the sensor is in a short circuitcondition. Similarly, if the sensed signal (μ) is at a minimum value,then the sensor may be deemed to be in an open circuit condition becausethe sensed value would be uncharacteristically low. Of course, theopposite may be true (a short circuit may provide a minimum value forthe sensed signal (μ) and an open circuit may provide a maximum valuefor the sensed signal (μ)), depending upon the polarity of the sensorsas installed or the configuration of the processing unit.

Once it is determined that one or more sensors have failed, thesesensors may be replaced easily and quickly. Alternatively, the entiresensor plug may be replaced with a new sensor plug having a new set ofsensors.

The processing unit 140 may be pre-programmed with a set of instructionsfor analyzing the vibration signals from the vibration sensor 166.According to one aspect, the vibration analysis method disclosed hereinis capable of determining the overall state or condition of the gearbox.According to another aspect, the vibration analysis method disclosedherein is capable of determining discrete component failures occurringwithin the gearbox. Referring now to FIGS. 12-14, and in particular toFIG. 12, at step 500, the processing unit 140 receives the vibrationsignal (μ_(V)) from the vibration sensor 166, which represents thevibration of the gearbox. The sensed signal (μ_(V)) is in the timedomain and may be denoted as (μ_(V)(t)), which may be analyzed withinthe time domain as will be discussed hereinafter. Next, at step 502, theprocessing unit 140 performs a Fourier Transform, which may be a FastFourier Transform, on the debiased and debiased-rectified vibrationsignal to obtain a vibration spectrum in the frequency domain, asfollows:

Y _(Vh)(f)=Re{Y _(Vh)(f)}+jIm{Y _(Vh)(f)}=FT{μ _(Vd)(t)} and FT{|μ_(Vd)(t)|}  [9]

where,

FT=Fourier transform

Y_(Vh)(f)=the Fourier transform of μ_(V)(t) and is complex-valued

μ_(Vd)(t)=debiased or dc-removed vibration signal in time, and

|μ_(Vd)(t)|=debiased-rectified vibration signal in time.

For the spectrum generation, the magnitude of Y_(Vh)(f) is generated by:

Y _(Vh-abs)(f)=|Y _(Vh)(f)|={square root over (Re{Y _(Vh)+L (f+L )}²+Im{Y _(Vh)+L (f+L )}²+L )}  [10]

The frequency axis is evaluated such as: $\begin{matrix}{{{f_{axis}(m)} = {{\frac{S_{adc}}{N_{spr2}}*\left( \left\lbrack \frac{m - N_{spr2} - 1}{2} \right\rbrack \right)_{{m = 1},\ldots \quad,{Nspr2}}} - \quad \left\lbrack {{- f_{m\quad a\quad x}},\ldots \quad,0,\ldots \quad,{+ f_{m\quad a\quad x}}} \right\rbrack}}\quad} & \lbrack 11\rbrack\end{matrix}$

where,

S_(adc)=Analog-to-digital converter sampling rate in Hertz;

N_(spr2)=A number of samples held in a buffer; and,

m=Index number representing a discrete location on the frequency axis.

Equation [11] indicates that there are negative and positive frequenciesin the spectrum with respect to zero frequency (DC component). Becausethe vibration signal is real-valued and the spectrum is symmetric withrespect to zero (DC) frequency, only the positive frequency spectrumdata may be used for any further analysis.

After evaluating Y_(Vh-abs)(f), a number of parameters, which may bemonitored for excessive vibration, may be determined. These parametersmay include the spectral component at zero frequency (DC), averagespectral energy within a band, and the maximum spectral peak within eachband. The generation of bands will be more fully described hereinafter.

At step 506, the spectral component at zero frequency is generated andis equal to the area under the time domain vibration signal. Thespectral component at zero frequency may be represented as:$\begin{matrix}{{Y_{{Vh} - {a\quad b\quad s}}\left( {f = 0} \right)} = {\int_{\infty}^{\infty}\left| {{\mu_{Vd}(t)}\quad {t}} \right.}} & \lbrack 12\rbrack\end{matrix}$

An excessive vibration will produce a large spectral component at zerofrequency. It should be appreciated that this parameter is readilyavailable after performing the Fast Fourier Transform of the vibrationsignal instead of actually integrating the signal. This parameter may bedenoted as V_(h-dc)(k), where (k) is the buffer location in theprocessing unit, and represents the area under the curve or themagnitude at zero frequency.

At step 508, the spectral component V_(h-dc)(k) is compared to one ormore thresholds (T_(oZ)) to determine whether excessive vibration isoccurring. At step 510, an alarm may be issued if excessive vibration isoccurring. As will be more fully described with reference to FIG. 14,the processing unit 140 may perform an analysis of the alarm signal inan effort to reduce the occurrence of false alarms.

Continuing with reference to FIG. 12, at step 514, the spectrum isdivided into N_(bin) bands, where N_(bin) is a power of 2 so that thespectrum can be equally divided linearly. FIG. 13 shows an example of adivided spectrum when the sampling rate (S_(adc))=25,000 Hz, the numberof bands (N_(bin))=8, and the number of data points (N_(spr2))=1,024.The average spectral energy and the maximum peak in each band aredetermined by the processing unit and are compared to separatethresholds. In this manner, the processing unit is able to detectwhether a peak amplitude and vibration energy of certain frequencies arepresent, indicating a defect or potential defect of a component in thegearbox because each component may exhibit discrete vibrationalcharacteristics at certain frequencies. Defects or potential defects ofdiscrete components may be analyzed independently, without the influenceof surrounding components. Otherwise, if the frequency spectrum isanalyzed without being divided into bands, then the vibrationalcharacteristics of discrete components may be dampened.

As will be further discussed hereinafter, the threshold within each bandmay be learned or set when the gearbox is placed in service, rather thanbeing pre-set and stored in memory. This feature, together with thefeature of dividing the spectrum into bands, allows for the detection ofdefects or potential defects exhibited by unknown or unpredictedfrequencies (i.e., components not normally recognized as exhibiting alikelihood of experiencing defects or a combination of components or acombination of the gearbox and surrounding equipment producing unknownor unpredicted frequencies). That is, if the spectrum is filtered, asmay be the case in some conventional monitoring systems, only predictedfrequencies remain. Thus, a particular frequency of a certain componentin combination with other components or surrounding equipment which maylie outside the predicted frequency, is not recognized and therefore isnot analyzed.

At step 516, a parameter representing the average spectral energy ineach band is generated using, for example, the following equation:$\begin{matrix}{{{V_{{e\quad r\quad g} - {sb}}\left( {k,l} \right)} = {\frac{1}{N_{sb}}*{\sum\limits_{i = {{{({l - 1})}*N_{sb}} + 1}}^{1*N_{sb}}\quad \left\lbrack {Y_{{Vh} - {a\quad b\quad s}}(i)} \right\rbrack^{2}}}},{l = 1},\ldots \quad,N_{bin}} & \lbrack 13\rbrack\end{matrix}$

where,

N_(sb)=N_(spr2)/N_(bin)

V_(erg-sb)(k,l)=the average energy in the l^(th) band in the k^(th)buffer signal.

At step 518, the average spectral energy (V_(erg-sb)(k,l) in each bandis compared to one or more thresholds (T_(ergZ,Nbin)). A certain levelof alarm (i.e. NORMAL, CAUTION, or WARNING, etc.) may be issued,depending upon which of the one or more thresholds are exceeded orcrossed. Alternatively, as shown in steps 520-522, a second tier ofcomparisons may be made before issuing an alarm. In this example, atstep 520, a value is assigned for each threshold crossing. If a firstthreshold is crossed, then a first value may be assigned to thatthreshold crossing; if a second threshold is crossed, then a secondvalue may be assigned, and so on, depending upon the number ofthresholds used. The numeric values for each band are summed together.At step 522, the summed values are then compared to energy thresholds(T_(eZ)). Depending upon which threshold (T_(eZ)) is exceeded, acorresponding level of alarm (i.e. NORMAL, CAUTION, or WARNING, etc.)may be indicated. Alternatively, as will be more fully described withreference to FIG. 14, the processing unit 140 may perform an analysis onthe alarm signal in an effort to reduce the occurrence of false alarms.

For example, assume there are three threshold levels for each band andthere are four bands. A crossing of the first threshold T_(erg1.N) mayhave a value of 0, a crossing of the second threshold T_(erg2,N) mayhave a value of 0.5 and the crossing of a third threshold T_(erg3,N) mayhave a value of 1. Assume that the average spectral energy(V_(erg-sb)(k,1)) for the first band has crossed the second thresholdT_(erg2), resulting in a numeric value 0.5, the average spectral energy(V_(erg-sb)(k,2)) for the second band has crossed the third threshold,resulting in a numeric value of 1, the average spectral energy(V_(erg-sb)(k,3)) for the third band has also crossed the thirdthreshold, resulting in a numeric value of 1, and the average spectralenergy (V_(erg-sb)(k,4)) for the fourth band has crossed the firstthreshold, resulting in a numeric value of 0 then the summed value is2.5. This summed value is compared to an energy threshold (T_(eZ)).Depending upon which threshold (T_(eZ)) is exceeded, a correspondinglevel of alarm may be indicated. Thus, in this example, assuming a valueof 0 is NORMAL, a value of 2 is CAUTION and a value of 4 is WARNING,then the processing unit 140 may indicate a CAUTION, even though, duringthe first level of comparisons, a higher level (i.e WARNING) may havebeen indicated. This second level of comparisons may be used to providean alarm for each parameter, which may be passed to aDiagnostic/Advisory/Decision (D/A/D) system, as will be explainedhereinafter.

Continuing with reference to FIG. 12, at step 528, a parameterrepresenting the spectral peak in each band is generated using, forexample the following equation:

V _(p-sb)(k,l)=max{Y _(Vh-abs)(i)}, i=(l−1)*N _(sb)+1 , . . . , l*N_(sb) ;l=1, . . . , N _(bin)  [14]

where,

N_(sb)=N_(spr2)/N_(bin)

V_(sb)=(k,l)=the peak spectrum in the l^(th) band in the k^(th) buffersignal.

As discussed above with reference to steps 518-526, the peak spectrum iscompared to a first level threshold and may be compared to a secondlevel threshold. Thus, at step 530, the spectral peak (V_(p-sb)(k,l)) ineach band is compared to one or more thresholds (T_(peakZ,Nbin)). Acertain level of alarm (i.e. NORMAL, CAUTION, or WARNING, etc.) may beissued depending upon which of the one or more thresholds are exceededor crossed.

As mentioned, a second tier of comparisons may be made before issuing analarm. Thus, at step 532, a value is assigned for each thresholdcrossing. If a first threshold is crossed, then a first value may beassigned to that threshold crossing; if a second threshold is crossed,then a second value may be assigned, and so on, depending upon thenumber of thresholds used. The numeric values for each band are summedtogether. At step 534, the summed values are then compared to peakthresholds (T_(pZ)). Depending upon which threshold (T_(pZ)) isexceeded, a corresponding level of alarm (i.e. NORMAL, CAUTION, orWARNING, etc.) may be indicated at step 536. Alternatively, as will bemore fully described with reference to FIG. 14, the processing unit 140may perform an analysis on the alarm signal in an effort to reduce theoccurrence of false alarms.

The peak vibration from the time domain and the overall energy from thetime domain may also be analyzed at steps 540 and 542, respectively. Thepeak vibration and the overall energy may then be compared to athreshold by a comparing each to a threshold at steps 544 and 546,respectively. Based on the comparison, alarms may be indicated at steps548 and 550, respectively. As above, the alarms generated may beanalyzed respectively, in a false alarm routine.

The above vibration analysis may also be useful in detecting damaginglevels of vibrations surrounding the working site of the gearbox.

In alternative embodiment, the processing unit 140 may provide theindividual alarms from the comparisons of the spectral component at zerofrequency, the average spectral energy in each band, the maximumspectral peak, the peak vibration in the time domain and the overallenergy in the time domain is indicated, to the D/A/D system, as shown atstep 560. These alarms may be used as input variables to the D/A/Dsystem, which comprises an expert system, for further analysis. TheD/A/D system may be used for diagnostic and advisory information for theoperator.

The processing unit 140 may be programmed with a set of instructions forlimiting the occurrence of false alarms. This may be accomplished, forexample, by performing a third tier analysis, such as, for example,averaging the alarm levels (i.e. averaging the number of occurrences ofNORMAL, CAUTION, or WARNING, etc.). In addition, the average alarmlevels for each parameter (spectral component at zero frequency, averagespectral energy in each band, spectral peak in each band, peakvibration, and overall energy) may be added together and compared to oneor more threshold values to obtain a global alarm indicative of theoverall condition of the gearbox, as shown in FIG. 14. Once the alarmsfor the individual parameters have been determined, at step 600, numericvalues are assigned to each alarm level. For example, NORMAL, CAUTION,and WARNING may be indicated with values of, for example, 0, 0.5, and 1,respectively. Next, at step 602, averages of a plurality (X) of numericvalues are determined. At step 604, these averages for each parameterare multiplied by a weighting factor and summed together. At step 606,the summed value is compared to one or more global thresholds (T_(gZ)).If the summed value exceeds the threshold, then a global alarm may beindicated at step 608. Of course, it is to be appreciated that the falsealarm rate may be adjusted by adjusting the number (X) of the numericvalues used in step 602, while maximizing detection probability of atrue alarm. In addition, or in the alternative, the global thresholds(T_(gZ)) may be adjusted to adjust the false alarm rate.

As discussed in connection with step 560 of FIG. 12, in an alternativeembodiment, the processing unit 140 may provide the averaged alarmvalues from step 602 to the D/A/D, shown at step 618.

A similar false alarm control scheme may be used for reducing falsealarms from the pressure sensor, the temperature sensor or any othersensors which may be used, while maximizing detection probability of atrue alarm. Such a scheme may include determining a weighted average ofthe indicated alarm levels prior to issuing an alarm, as above. As bestshown in FIG. 15, after the alarms for the individual parameters havebeen determined at step 680, then, at step 682, numeric values areassigned to each alarm level. For example, NORMAL, CAUTION, and WARNINGmay be indicated with values of, for example, 0, 0.5, and 1,respectively. Next, at step 684, an average of a plurality (X) ofnumeric values is determined. At step 686, the average is compared toone or more thresholds. At step 688, the indicated alarm level NORMAL,CAUTION, or WARNING may be indicated. The false alarm rate may beadjusted by adjusting the number (X) of the numeric values used in step684. In addition, or in the alternative, the thresholds may be adjustedto adjust the false alarm rate. The processing unit 140 may provide theaveraged alarm value from step 682 and/or step 684 to the D/A/D.

According to another aspect of the invention, it may be desirable to setthe any or all of the above mentioned thresholds when the gearbox isplaced in its working environment rather than pre-setting the thresholdlevels during manufacture of the gearbox. Thus, the operatingenvironment surrounding the working site the of the gearbox may be takeninto account. As shown in FIG. 16, the thresholds may be learned by theprocessing unit 140. In this example, at step 700, a learning time(t_(L)) may be provided by the user or a predetermined learning time maybe stored in the memory of the processing unit. During the learning time(t_(L)), the sensed conditions (μ) are accumulated in the memory. Atstep 702, one or more buffers (M) are provided. At step 704, M values ofthe following seven parameters are established: μ_(T-oil) (k), μ_(P-oil)(k), V_(h-peak) (k), V_(h-erg) (k), V_(h-dc) (k), V_(erg-sb) (k,1), andV_(p-sb) (k,1), where k=1 through M. In the example described herein,the first four parameters are produced from the pre-processing of thetime signals from the temperature, pressure, and vibration sensors andthe other three parameters are generated from the vibration analysisusing the vibration signal only. Of course, other parameters values maybe acquired, depending upon other sensors that may be added to orsubstituted into the monitoring system. To determine the thresholds, atstep 706, the mean (m) and standard deviation (S) of each of theseparameters are evaluated using, for example, the following equations:$\begin{matrix}{{{m_{T - {oil}} = {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad {\mu_{T - {oil}}(i)}}}};{and}},} & \lbrack 15\rbrack \\{S_{T - {oil}} = \left\lbrack {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad \left\{ {{\mu_{T - {oil}}(i)} - m_{T - {oil}}} \right\}^{2}}} \right\rbrack^{\frac{1}{2}}} & \lbrack 16\rbrack \\{{{m_{P - {oil}} = {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad {\mu_{P - {oil}}(i)}}}};{and}},} & \lbrack 17\rbrack \\{S_{P - {oil}} = \left\lbrack {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad \left\{ {{\mu_{P - {oil}}(i)} - m_{P - {oil}}} \right\}^{2}}} \right\rbrack^{\frac{1}{2}}} & \lbrack 18\rbrack \\{{{m_{{Vh} - {peak}} = {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad {V_{h - {peak}}(i)}}}};{and}},} & \lbrack 19\rbrack \\{S_{{Vh} - {peak}} = \left\lbrack {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad \left\{ {{V_{h - {peak}}(i)} - m_{{Vh} - {peak}}} \right\}^{2}}} \right\rbrack^{\frac{1}{2}}} & \lbrack 20\rbrack \\{{{m_{{Vh} - {e\quad r\quad g}} = {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad {V_{h - {e\quad r\quad g}}(i)}}}};{and}},} & \lbrack 21\rbrack \\{S_{{Vh} - {e\quad r\quad g}} - \left\lbrack {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad \left\{ {{V_{h - {e\quad r\quad g}}(i)} - m_{{Vh} - {e\quad r\quad g}}} \right\}^{2}}} \right\rbrack^{\frac{1}{2}}} & \lbrack 22\rbrack \\{{{m_{{Vh} - {d\quad c}} = {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad {V_{h - {d\quad c}}(i)}}}};{and}},} & \lbrack 23\rbrack \\{S_{{Vh} - {d\quad c}} - \left\lbrack {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad \left\{ {{V_{h - {d\quad c}}(i)} - m_{{Vh} - {d\quad c}}} \right\}^{2}}} \right\rbrack^{\frac{1}{2}}} & \lbrack 24\rbrack \\{{{{m_{{e\quad r\quad g} - {sb}}(l)} = {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad {V_{{e\quad r\quad g} - {sb}}\left( {i,l} \right)}}}};{and}},} & \lbrack 25\rbrack \\\left. {{S_{{e\quad r\quad g} - {sb}}(l)} = {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad \left\{ {{V_{{e\quad r\quad g} - {sb}}\left( {i,l} \right)} - {m_{{e\quad r\quad g} - {sb}}(l)}} \right\}^{2}}}} \right\rbrack^{\frac{1}{2}} & \lbrack 26\rbrack \\{{{{m_{{vp} - {sb}}(l)} = {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad {V_{p - {sb}}\left( {i,l} \right)}}}};{and}},} & \lbrack 27\rbrack \\{{S_{{vp} - {sb}}(l)} = \left\lbrack {\frac{1}{k}{\sum\limits_{i = 1}^{k}\quad \left\{ {{V_{p - {sb}}\left( {i,l} \right)} - {m_{{vp} - {sb}}(l)}} \right\}^{2}}} \right\rbrack^{\frac{1}{2}}} & \lbrack 28\rbrack\end{matrix}$

where l=1, . . . , N_(bin), _(T-oil) and _(P-oil) (as subscripts)represent a value relating to the temperature of the oil and thepressure of the oil, respectively. The thresholds for the alarms arecomputed at step 708 using, for example, the following equations:

t(n)=m+n*S  [29]

where,

t=the learned thresholds and,

n=threshold number.

According to another aspect of the invention, the monitoring system 100may also be used to determine whether the gearbox may be operated closerto its physical operating limit, thereby handling more power or speedwithout the need to modify the physical design. Referring specificallyto FIG. 17, at step 800, the operating conditions of the gearbox (suchas temperature, pressure, or vibration) are sensed by the monitoringsystem as described above, although other conditions may be sensed asdesired. Next, at step 802, the sensed operating conditions are comparedto threshold values, also as described above. In this manner, thethresholds may define the physical operating limits of the gearbox. Atstep 804, the processing unit determines the margin of safety betweenthe sensed values and the thresholds. This margin indicates the amountof increase in load that the gearbox may experience before thethresholds are exceeded. Thus, at step 806, the processing unitindicates a percentage increase in load to an operator, whichcorresponds to the margin. An operator may then increase the load by theindicated percentage, which has the effect of reducing the margin.Alternatively, the processing unit may communicate with a controller onthe machine that is coupled to the gearbox. The processing unit may thensignal the machine controller to modify its output to the gearboxaccordingly.

According to another aspect of the invention, torque estimation may beperformed by determining the number of discrete samples representing arotation of a rotating member of the gearbox, such as the input shaft,and comparing the number of discrete samples to stored datarepresentative of the number of discrete samples as a function oftorque, as will be described. A percent change in the number of discretesamples indicates a corresponding percent change in torque. The numberof discrete samples may be determined through the use of one or moreconventional sensors and a relationship between the number of discretesamples and torque may be obtained through experimentation. As shown inFIG. 1, an example of such a sensor may be a Hall effect transducer 900communicating with a toothed ring (not shown) or a notch (not shown) onthe input shaft.

FIG. 18 shows an example of a method performed by the processing unitaccording to this aspect of the invention. In this example, the numberof discrete samples representing a shaft rotation is determined byanalyzing the samples generated by the analog-to-digital converter onthe sensor. It is to be appreciated that the analog-to-digital convertersamples the sensor at a predetermined sampling frequency. At step 901, anumber (M) of buffer samples from the sensor 900 is accumulated inmemory. Next, at step 902, the number of revolutions that are in the Mbuffer samples is obtained, and at step 904, the number of samples perrevolution of the sensor performed by the analog-to-digital converter(i.e the number of samples occurring between complete revolutions) isaccumulated. This may be accomplished because the number of samplesperformed by the analog-to-digital converter between completerevolutions of the shaft is greater than the rate at which the sensorindicates a complete revolution. Thus, the higher the number of samplesbetween revolutions, the slower the frequency of rotation. At step 906,the minimum (N_(min)), mean (N_(mean)) and maximum (N_(max)) number ofsamples per revolution are computed. At step 908, an estimated torquethat is applied to the gearbox is computed. This may be accomplished byusing a look-up table or curve or a suitable functional relationshipstored in memory that relates the number of samples per revolution totorque. Torque data as a function of the number of samples perrevolution may be determined by experimentation of a test gearbox. Anexample of such a relationship is shown in FIG. 19. Rather than using alook-up table, a suitable function may be derived from the experimentaldata using, for example, curve fitting techniques, such as the leastsquares method or non-linear data-fitting methods.

An example of such a functional relationship is:

%L=C ₁ N ² +C ₂ N ₂ +C ₃  [30]

where,

C₁, C₂ and C₃ are constants;

N=Number of samples per revolution, which may be N_(min), N_(mean),N_(max); and,

%L=Estimated percent load or torque.

The estimated torque applied to the shaft may be determined to beapproximately equal to the torque derived from the mean number ofsamples per revolution (N_(mean)), bounded by a maximum and a minimumtorque, derived from the maximum and minimum number of samples perrevolution (N_(max), N_(min)), respectively. At step 912, estimatedtorque as a percent load may be output to the indicator 149 (see FIG.1), or used or displayed in any desired manner. Preferably, thecomputation described with reference to FIG. 18 is repeated during theoperation of the gearbox.

If the percent load estimated by one of the methods described above is atorque applied to a motor that is coupled to and drives a gearbox, thepercent load (or torque) applied to the gearbox output shaft can also beestimated. The torque applied to the gearbox output shaft is directlyproportional to that applied to the motor shaft. The torque applied tothe motor shaft (%L_(motor shaft)) is less than the torque applied tothe output shaft of the gearbox (%L_(gearbox output shaft)). Thisrelationship holds because of the efficiency of the gearbox(η_(gearbox)). This efficiency may be obtained from the gearboxmanufacturer, a look-up table of efficiency as a function of speed, orother suitable parameters relating to the motor and/or the gearbox. Thetorque applied to the output shaft of the gearbox may be determined by:

%L _(gearbox output shaft)=%L _(motor shaft)*η_(gearbox)  [31]

Alternatively the torque applied to the output shaft of the gearbox maybe determined by the following equation:

%L _(gearbox output shaft) =L _(motor shaft)−(1−η_(gearbox))  [32]

According to another aspect of the present invention, the gearbox may beactively controlled to increase performance and efficiency, without theneed to replace the gearbox with a gearbox designed specifically for theincreased demand.

In a preferred embodiment, this may be accomplished by the methoddescribed with reference to FIG. 20. At step 1000, the operatingconditions of the gearbox are sensed using for example the sensors andmethodology described above. The sensed conditions, at step 1002, arecompared to the threshold values also, as described above. In addition,or in the alternative, the sensed operating conditions may be comparedto external conditions to the gearbox. Such external conditions may bethe torque applied to the input shaft of the gearbox, as shown at step1004. If the threshold values or the external conditions to the gearboxare exceeded, then, at step 1006, the processing unit sends signals tovarious actuators to adjust certain operating characteristics of thegearbox. Examples of such adjustments are discussed with reference tosteps 1008, 1010, 1012, and 1014.

At step 1008, the gearbox may include an oil injector 1020 positionedeither in an additional oil drain plug or in a separate opening formedin the case of the gearbox (as shown in FIG. 1) and communicating withthe processing unit. The oil injector may be adapted to inject oil ontothe gear mesh or onto any suitable rotating member within the gearbox.In addition, the oil injector may simply be used to increase the oillevel within the gearbox. Of course, one or more oil injectors may beused. Thus, according to this aspect of the invention, if the oil level,as sensed in step 1000, is below a threshold value, as compared in step1002, then, at step 1008, the processing unit may send a signal to theoil injector to inject additional oil into selected areas within thegearbox.

Another example of adjusting operating characteristics within thegearbox is shown at step 1010. In this step, the gearbox may be cooledso as to lower the operating temperature to within the limitsestablished by the threshold. Examples of gearbox cooling include, butare not limited to, spraying cooling liquid onto the gearbox itself,operating a cooling fan to provide air cooling over the gearbox orfitting the gearbox with liquid channels formed in the case andconnecting the channels to a suitable climate control unit. The gearboxmay also be heated if the operating temperature is not operating above athreshold. Accordingly, warm air may be moved over the gearbox, or thegearbox may be fitted with an electrical heater. Also, warm liquid mayflow through the channels formed in the gearbox case.

In some instances, the input torque to the gearbox may change, which mayrequire an adjustment to the gearbox to accommodate the increasedstrength requirements. Accordingly, as shown at step 1012, materialproperties, such as the stiffness, of the gearbox components may bevaried using suitable material property adjusting techniques now knownor later developed. Examples of such techniques include using adaptiveor intelligent materials, such as materials having fibers embeddedtherein which are responsive to electric fields applied thereto. Othermethods may include piezoelectric or magnetorheological techniques. Suchan adjustment to the material properties may avoid shock damage orsmooth out mechanical power transfer through the gearbox.

If the sensed operating condition is vibration, and the vibrationexceeds a threshold, then, at step 1014, vibration or noise cancellationtechniques may be applied to the gearbox such that the detrimentalvibration may be canceled.

Other suitable methods may be used to control the operatingcharacteristics of the gearbox to improve the performance or efficiencythereof.

While the best mode for carrying out the invention has been described indetail, those skilled in the art to which this invention relates willrecognize various alternative embodiments including those mentionedabove as defined by the following claims.

What is claimed is:
 1. An apparatus comprising: a gearbox having atleast one rotating component; and a sensor plug coupled to the gearboxto sense a plurality of operating conditions of the gearbox, said sensorplug comprising: a plug body; a probe end formed at one end of said plugbody, said probe end mounted to the gearbox; and a plurality of sensorslocated entirely within said plug body, said plurality of sensorscomprising a first sensor sensing a first operating condition of thegearbox and a second sensor sensing a second operating condition of thegearbox, with the first operating condition being different from thesecond operating condition.
 2. An apparatus according to claim 1 furthercomprising a well formed at another end of said plug body opposite saidprobe end, with at least one of said plurality of sensors being locatedwithin said well.
 3. An apparatus according to claim 2 furthercomprising a pressure port extending from said well and through saidprobe end.
 4. An apparatus according to claim 3 wherein one of saidplurality of sensors is a pressure sensor communicating with saidpressure port.
 5. An apparatus according to claim 4 further comprising adiaphragm mounted between said pressure sensor and said pressure port.6. An apparatus according to claim 4 wherein said pressure port includesan incompressible fluid sealed therein, with said pressure sensor beingresponsive to pressure changes induced on said incompressible fluid. 7.An apparatus according to claim 2 wherein said well is filled with apotting material to encapsulate said sensors.
 8. An apparatus accordingto claim 7 further comprising an ambient pressure port formed throughsaid potting material, with said pressure sensor communicating with saidambient pressure port.
 9. An apparatus according to claim 7 furthercomprising a retainer for retaining said potting material within saidwell.
 10. An apparatus according to claim 9 wherein said well defines anaxially extending sidewall, with said sidewall having said retainerformed therealong for axially retaining said potting material withinsaid well.
 11. An apparatus according to claim 10 wherein said sidewallis formed with a coarse surface, thereby defining said retainer.
 12. Anapparatus according to claim 10 wherein said sidewall includes aradially inwardly extending lip, thereby defining said retainer.
 13. Anapparatus according to claim 2 further comprising a shoulder formedbetween said probe end and said well, with said shoulder beingconstructed and arranged to axially support a housing for housing aprocessing unit such that said well will extend into the housing.
 14. Anapparatus according to claim 13 further comprising a seal disposedadjacent said shoulder, with said seal being adapted for sealing againstthe housing.
 15. An apparatus according to claim 13, in combination withthe housing.
 16. A combination according to claim 15 further comprisinga processing unit mounted within said housing, with each said sensorhaving at least one electrical lead emerging from said well and beingconnected directly to said processing unit, with each said lead beinghoused entirely within said housing.
 17. An apparatus according to claim2 further comprising a pressure port extending from said well to saidprobe end such that said pressure port is a blind hole defining arelatively thin wall section, with said pressure sensor being mounted tosaid thin wall section.
 18. An apparatus according to claim 1 whereinsaid pressure sensor also communicates with ambient pressure.
 19. Anapparatus according to claim 1 further comprising a temperature portextending from said well to said probe end.
 20. An apparatus accordingto claim 19 wherein one of said plurality of sensors is a temperaturesensor disposed within said temperature port, with said temperature portbeing adapted to position said temperature sensor to sense one of an oiltemperature and a case temperature of the gearbox.
 21. An apparatusaccording to claim 19 wherein said temperature port extends through saidprobe end, with said sensor plug further comprising a temperature portplug inserted into and extending partially within said temperature port.22. An apparatus according to claim 21 wherein said temperature portplug is formed of a thermally conductive material.
 23. An apparatusaccording to claim 2 wherein one of said plurality of sensors is avibration sensor.
 24. An apparatus according to claim 23 wherein saidvibration sensor is mounted in said well.
 25. An apparatus according toclaim 1 in combination with a housing mounted on said sensor plug withsaid sensor plug supporting said housing in a spaced relation away fromsaid gearbox.
 26. An apparatus according to claim 1 wherein said probeend is adapted for communication with an oil reservoir of said gearbox.27. An apparatus according to claim 1 wherein said probe end is adaptedfor attaching to an oil drain hole formed in said gearbox.
 28. Anapparatus according to claim 1 wherein said body is formed of at leastone material selected from the group consisting of metal, plastic andceramic.
 29. An apparatus according to claim 1 wherein said probe endextends into a wall of said gearbox without extending beyond the innerwall surface of the gearbox.
 30. An apparatus according to claim 1 withsaid probe end extending through a wall of said gearbox and beyond theinner wall surface of the gearbox, with said sensors being adapted tocommunicate exclusively with the processing unit.
 31. A sensor plug foruse in sensing a plurality of operating conditions of a devicecomprising: a plug body; a probe end formed at one end of said plugbody, said probe end being adapted for attaching to the device; a wellformed at another end opposite said probe end; a vibration sensordisposed in said well; a pressure port extending from said well andthrough said probe end; a pressure sensor disposed within said well andcommunicating with said pressure port for sensing liquid pressure withinthe device; a temperature port extending from said well to said probeend; a temperature sensor disposed within said temperature port forsensing liquid temperature within the device; and a shoulder formedbetween said probe end and said well, with said shoulder being adaptedfor axially supporting a housing for housing a processing unit such thatsaid well will extend into the housing; wherein said well is filled witha solid potting material to encapsulate said sensors.
 32. A sensor plugaccording to claim 28 wherein said pressure sensor also communicateswith ambient pressure.
 33. A sensor plug according to claim 28 whereinsaid temperature port extends through said probe end, with said sensorplug further comprising a temperature port plug inserted into andextending partially within said temperature port.
 34. A sensor plugaccording to claim 3 wherein said temperature port plug is formed of athermally conductive material.
 35. A sensor plug according to claim 28further comprising a seal disposed adjacent said shoulder, with saidseal being adapted for sealing against the housing.
 36. A sensor plugaccording to claim 31 combination with the device and the housing, withsaid device being a gearbox, and a processing unit, with said sensorplug supporting said housing in a spaced relation away from saidgearbox.
 37. A sensor plug according to claim 31 wherein said probe endis adapted for attaching to an oil drain hole formed in said gearbox.38. A sensor plug according to claim 31 in combination with the device,with said probe end extending into a wall of said device withoutextending beyond the inner wall surface of the device.
 39. A sensor plugaccording to claim 31 in combination with the device, with said probeend extending through a wall of said device and beyond the inner wallsurface of the device, with said sensors being adapted to communicateexclusively with the processing unit.
 40. A sensor plug according toclaim 31 further comprising a diaphragm mounted between said pressuresensor and said pressure port.
 41. A sensor plug according to claim 31wherein said pressure port includes an incompressible fluid sealedtherein, with said pressure sensor being responsive to pressure changesinduced on said incompressible fluid.
 42. A system for sensing aplurality of operating conditions of a device comprising: a plug bodyconstructed and arranged to mount to the device; a plurality of sensorslocated entirely within said plug body, said plurality of sensorscomprising a first sensor sensing a first operating condition of thedevice and a second sensor sensing a second operating condition of thedevice, with the first operating condition being different from thesecond operating condition; a support formed on said plug body; ahousing mounted to said plug body and supported by said support; and, aprocessing unit disposed within said housing and communicating with saidplurality of sensors; wherein one of said plurality of sensors is apressure sensor capable of responding to changes in a sensed pressurerelative to atmospheric pressure.
 43. A sensor plug for use in sensing aplurality of operating conditions of a device comprising: a plug body; aprobe end formed at one end of said plug body, said probe end beingadapted for mounting to the device, a plurality of sensors locatedwithin said plug body, said plurality of sensors comprising a firstsensor sensing a first operating condition of the device and a secondsensor sensing a second operating condition of the device, with thefirst operating condition being different from the second operatingcondition; and a well formed at another end of said plug body oppositesaid probe end, with at least one of said plurality of sensors beinglocated within said well, wherein said well is filled with a solidpotting material to encapsulate said sensors.
 44. A sensor plugaccording to claim 43 further comprising an ambient pressure port formedthrough said potting material, with at least one of said plurality ofsensors being a pressure sensor communicating with said ambient pressureport.
 45. A sensor plug according to claim 43 further comprising aretainer for retaining said potting material within said well.
 46. Asensor plug according to claim 45 wherein said well defines an axiallyextending sidewall, with said sidewall having said retainer formedtherealong for axially retaining said potting material within said well.47. A sensor plug according to claim 46 wherein said sidewall is formedwith a coarse surface, thereby defining said retainer.
 48. A sensor plugaccording to claim 46 wherein said sidewall includes a radially inwardlyextending lip, thereby defining said retainer.
 49. A sensor plug for usein sensing oil pressure in a device comprising: a plug body having afirst end and a second end; a probe end formed at said first end of saidbody; a pressure sensor port extending substantially between said probeend and said second end of said body; an incompressible fluid sealedwithin said pressure sensor port; and, a pressure sensor responsive topressure changes of said incompressible fluid relative to atmosphericpressure.